This invention relates to exhaust systems and in particular, to a muffler for controlling and reducing noise associated with engine exhaust gas. More particularly, this invention related to a muffler having internal stamped sheet metal tuning plates and drop-in baffles fixed inside a muffler chamber formed by two mating external shells.
For several years, mufflers have been constructed using stamp-formed sheet metal shells, plates, and baffles. Although conventional stamped mufflers can be assembled using fewer component parts than conventional tube mufflers, it is nevertheless recognized that it is necessary to modify the design of conventional stamped mufflers to improve the manufacturability of stamped mufflers. For example, it has been observed that weld process time for assembling conventional stamped mufflers is high and that it is often necessary to rely on costly, space-consuming, and labor-intensive welding equipment to attach conventional stamped muffler components together. It will be appreciated that the unit cost of each stamped muffler can rise significantly if the weld process time allocated for muffler assembly is very large.
It has also been observed that conventional mufflers are not generally configured to help dissipate any condensate that develops in cooler regions of the muffler chamber during passage of hot exhaust gases therethrough. Of course, development of any condensate pools or puddles along an interior wall of the muffler chamber can lead to rust or other corrosive damage to the muffler itself and possibly to development of muffler leakage problems. Moreover, a pool of condensate can freeze in the muffler chamber or its internal passageways during cold weather and block the flow of exhaust gas through the muffler to such an extent that a vehicle engine connected to the muffler cannot be started.
All mufflers vibrate quite a lot during use because of irregular pulsation of high-temperature, vehicle exhaust gas conveyed through the muffler chambers and passageways. Such pulsations are known to vary between 25 and 300 cycles per second in an irregular pattern and create muffler shell vibration and noise. Stamped mufflers are particularly susceptible to excessive shell noise problems due, in part, to a lack of adequate internal support structure for the muffler shells.
One object of the present invention is to provide a muffler assembly made of stamp-formed components which can be assembled quickly and easily without using costly complex welding techniques.
Another object of the present invention is to provide a muffler assembly with condensate delivery channels for conducting any condensate that develops in a cool region of the muffler to a drainage outlet or to relatively hotter muffler region so that the condensate will evaporate and become entrained in the flow of hot exhaust gas exiting the muffler upon exposure to the higher heat in the relatively hotter muffler region.
Yet another object of the present invention is to provide a muffler assembly that is constructed to reduce shell noise associated with vibration occurring during muffler use.
According to the present invention, a muffler assembly includes a first shell half and a second shell half attached to the first shell half at a perimetrically extending split line to define a muffler chamber therebetween. The first and second shell halves cooperate to define a flange-receiving space therebetween at the split line. An inlet port is provided in the muffler assembly for admitting exhaust gas into the muffler chamber and an outlet port is also provided for expelling exhaust gas from the muffler chamber.
A first tuning plate is disposed in the muffler chamber. The first tuning plate has a flange edge trapped in the flange-receiving space to retain the first tuning plate in a fixed position dividing the muffler chamber into a first chamber between the first tuning plate and the first shell half and a second chamber between the first tuning plate and the second shell half. A second tuning plate is also disposed in the second chamber. The second tuning plate cooperates with the first tuning plate to define exhaust gas-conducting tubes connected to the muffler chamber inlet and outlet. Means is provided for attaching the second tuning plate to the first tuning plate in piggyback relation to provide the exhaust gas-conducting tubes and to retain the second tuning plate in mating engagement with the first tuning plate without extending into the flange-receiving space at the split line so that only the first shell half, second shell half, and first tuning plate are rigidly joined together at the split line.
In preferred embodiments, each of the first and second shell halves and the first tuning plate include a perimetrically extending flange or skirt which are arranged to lie in side-by-side relation with the first tuning plate flange sandwiched between the spaced-apart shell half skirts upon assembly of the stamp-formed components comprising the muffler assembly. This three-layer sandwich of sheet metal flanges is mechanically locked using a press to define a perimetrically extending rolled seam connection situated outside of the muffler chamber. Advantageously, the number of sheet metal layers which need to be locked together is minimized using this design.
It will be appreciated that the difficulty associated with mechanically locking or welding sandwiched layers of sheet material together increases every time an additional layer of sheet material is added to the sandwich. Accordingly, attachment of the second tuning plate directly to the first tuning plate in piggyback relation without arranging the second tuning plate as a fourth layer to be mechanically locked or welded to the shell half skirts and the first tuning plate flange can lead to improved manufacturability of a muffler assembly.
In preferred embodiments of the invention, each shell halve is formed to include a longitudinally extending, internal delivery channel configured to conduct condensate from one point to another in the muffler chamber. Each shell half is also formed to include a plurality of transversely extending tributary channels aligned in spaced-apart relation to intersect the longitudinally extending delivery channel at spaced points along its length. While some of these tributary channels will receive mounting flanges of drop-in, flow-control baffles installed in the muffler chamber between one of the shell halves and one of the tuning plates, at least one of the tributary channels will be arranged to extend into a condensate-developing region to collect condensate developed therein and feed such collected condensate into the longitudinally extending delivery channel for delivery to a destination or drain outlet in the muffler assembly. Not only do those channels provide an elongate draining or collecting function, but they also serve to stiffen the outer shells, thereby reducing shell noise caused by vibration during muffler use.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.